Control of the rhizobium–legume symbiosis by the plant nitrogen demand is tightly integrated at the whole plant level and requires inter-organ systemic signaling

Summary

This review synthesises current understanding of how legume plants regulate their symbiotic relationship with nitrogen-fixing rhizobia in response to whole-plant nitrogen and carbon demands. Drawing on split-root experiments, biochemical analysis, and genetic studies, the authors describe multiple parallel systemic signalling pathways that control nodule development and function, with rapid adjustments to nodule carbohydrate availability serving as a key regulatory mechanism. The work highlights that symbiotic capacity is tightly adjusted to mineral nitrogen availability and photosynthetic performance, though the specificity of these mechanisms relative to non-symbiotic root development remains incompletely understood.

UK applicability

These mechanistic insights into legume–rhizobia symbiosis are relevant to UK agricultural practice, particularly in organic and low-input farming systems where biological nitrogen fixation reduces dependence on synthetic fertilisers. Understanding how environmental stresses impair symbiotic activity and how plants compensate could inform breeding programmes and crop management in UK temperate climates.

Key measures

Nodule organogenesis, nodule sugar levels, systemic nitrogen-satiety and nitrogen-deficit signalling, nodule senescence rates, transcriptomic and metabolomic profiles, sucrose allocation patterns

Outcomes reported

The study investigated regulatory mechanisms controlling nodule formation, functioning, and senescence in response to plant nitrogen demand using split-root systems and multi-omics approaches. It identified systemic signalling pathways and their molecular components that coordinate symbiotic nitrogen fixation with whole-plant nutritional status.

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